A press of pressure cell type generally comprises a force-absorbing press body which defines a press chamber. In the upper part of the press chamber, a press plate and a diaphragm of rubber or another resilient material are arranged, which together form a pressure cell. The pressure cell communicates with a source of pressure and expands when a pressure medium is supplied. In the lower part of the press chamber, a structural support or a tray is arranged, which comprises a bottom plate having a tray frame. The tray supports a forming tool, a workpiece, a mat of rubber or another resilient material, covering the forming tool and the workpiece.
Presses of pressure cell type are used, among other things, when forming sheet-shaped blanks, for example sheets of steel or aluminium, for short series products within the aircraft industry and the motor industry. The sheet is placed in the press in such a manner that one of its sides faces a forming tool. The resilient diaphragm is arranged on the other side of the sheet. A closed space between the diaphragm and the press plate located above the diaphragm constitutes the pressure cell and this space is filled during the forming process with a pressure medium. By pumping additional pressure medium into the pressure cell, the pressure is increased in the pressure cell and the resilient diaphragm is pressed during stretching against the sheet which, in its turn, is formed round or in the forming tool. When the sheet completely fits to the tool, the pressure in the pressure cell is released and the diaphragm is removed, after which the formed component can be taken out of the press.
Another field in which presses of pressure cell type are used is wood compaction when a workpiece of wood is exposed to high pressure, either in a forming tool or on its own. Reasons for compacting wood are, for example, that it is desirable to increase the hardness of the wood, decrease the moisture content or to obtain a phase in pressure impregnation.
A diaphragm which is used in presses of pressure cell type has a limited service length, which means that the diaphragm has to be exchanged at certain time intervals. The diaphragms are often difficult to remove and, therefore, the exchanging process is both laborious and time-consuming. One example which illustrates these disadvantages is obtained from SE 404 140 which relates to a press, a diaphragm being arranged round an attaching frame that is attached to an attaching means with the aid of a number of bolts. Those skilled in the art will realise that exchanging a diaphragm in such a construction is very complicated.